Method for the uniform preparation of silver halide grains

ABSTRACT

1. A METHOD AND APPARATUS FOR ITS PRACTICE ARE DISCLOSED WHERE, UNIFORMLY SIZED SILVER HALIDE GRAINS ARE PRECIPITATED IN AN AQUEOUS PEPTIZER SOLUTION BY THE REACTION OF A SILVER SALT SOLUTION WITH A HALIDE SALT SOLUTIONS, WHERE AT LEAST ONE OF THE SOLUTIONS HAS BEEN MIXED WITH A PORTION OF THE PEPTIZER SOLUTION PRIOR TO ITS REACTION WITH THE OTHER SLUTION WITHIN THE REMAINDER OF THE PEPTIZER SOLUTION, APPARATUS IS DISCLOSED FOR PRACTICING THE METHOD OF THIS INVENTION INCLUDING AT LEAST ONE SEPARATE MIXING CHAMBER FOR   DILUTION OF A SLAT SOLUTION WITH A PORTION OF THE PEPTIZER SOLUTION PRIOR TO THE PRECIPITATION REACTION.

Jan. 1, 1974 PORTER EIAL 3,782,954

METHOD FOR THE UNIFORM PREPARATION OF SILVER HALIDE GRAINS Original Filed Nov. 14, 1969 2 Sheets-Sheet L Jan. 1, 1974 PORTER ETAL 3,782,954

METHOD FOR THE UNLFORM PREPARATION OF SILVER HALIDE GRAINS 2 Sheets-Sheet 2 Original Filed Nov. 14, 1969 United States Patent O METHOD FOR THE UNIFORM PREPARATION OF Int. Cl. G03c 1/02 US. Cl. 96-94 2 Claims ABSTRACT OF THE DISCLOSURE A method and apparatus for its practice are disclosed where, uniformly sized silver halide grains are precipitated in an aqueous peptizer solution by the reaction of a silver salt solution with a halide salt solution, where at least one of the solutions has been mixed with a portion of the peptizer solution prior to its reaction with the other solution within the remainder of the peptizer solution. Apparatus is disclosed for practicing the method of this invention including at least one separate mixing chamber for dilution of a salt solution with a portion of the peptizer solution prior to the precipitation reaction.

This is a continuation of application Ser. No. 876,893, filed Nov. 14, 1969 and now abandoned.

This invention relates to an improved method for the preparation of silver halide crystals and to apparatus useful in the practice of this method.

In the preparation of silver halide type photographic emulsions it is often desirable that the silver halide crystals or grains used therein being a finely divided form. Preparation of finely divided silver halide has normally been accomplished by the precipitation of the silver halide grains by means of a so-called double decomposition reac tion in an aqeous solution of a colloidal, aqueous peptizer solution, for example, an aqueous gelatin solution. Two convenient methods for performing the double decomposition reaction are characterized by the manner of introduction of the reactants, i.e., by single jet or double jet means. A thorough discussion of these methods of reaction can be found in the following references: Photographic Chemistry, Pierre Glafkides, Fountain Press, London, 1958, pp. 327-330; Nucleation in Silver Bromide Precipitation, C. R. Berry and D. C. Skillman, J. Phys. Chem, 68, 1138- 43 (1964); and The Theory of the Photographic Process, 3rd ed., C. E. K. Mees and T. H. James MacMillan, 1966, chapter 2, p. 34. Emulsions made by these techniques are now referred to as single jet or double jet emulsions.

In preparing a typical double jet emulsion, an aqueous solution of a water soluble silver salt and an aqueous solution of a water soluble halide are added simultaneously to the aqueous peptizer solution. As the resultant silver halide grains are precipitated, the individual grain size normally tends to vary widely, particularly during the preparation of fine grain emulsions. In general, nonuniformity in the size of the precipitated silver halide grains caused by aggregation of grains and the like imparts adverse photographic characteristics to the photographic materials produced therefrom. For example, clumped or aggregate crystals tend to develop spontaneously causing an undesirable phenomenon known as pepper fog. Typical emulsions prepared with silver halide Patented Jan. 1, 1974 grains precipitated by the single jet method can likewise exhibit the aforementioned adverse characteristics.

There have been several attempts to produce silver halide grains having a narrow grain size distribution, i.e., a substantially uniform size throughout. Specifically, emulsions have been prepared which contain substantially fewer non-uniform large grains than were possible with the older precipitation techniques. Exemplary of the improvements in silver halide precipitation techniques are US. Pat. 2,996,287 and Us. 3,415,650. These patents, respectively, disclose an apparatus and the method for improving the dispersion of a salt solution into a peptizer solution and a method of removing reaction product from a reaction zone so as to diminish the possibilities for crystal aggregate formation.

While the aforementioned apparatus and method were achievements in overcoming some of the drawbacks related to double jet and single jet precipitations, limitations in these methods have produced problems. For example, it is not possible to achieve greater production from existing apparatus by increasing the concentration of the reactants without increasing the resultant grain size distribution and thereby producing pepper fog.

Fine grain photographic emulsions containing silver halide grains prepared according to the method and apparatus of this invention, are substantially free of nonuniform large grains and the resultant product is free of pepper fog. Such emulsions exhibit better high light contrast and sharpness than heretofore. These characteristics are particularly desirable in multicolor materials where local ill effects from aggregate grains are damaging to image quality.

Production of coarser grain emulsions, particularly of the single jet type are also improved by the method of this invention. Greater concentrations of reactants can be handled in emulsion preparation while experiencing a substantial reduction in the population of aggregate grains produced.

The aforementioned advantages have been achieved, i.e., non-uniform grain formation has been substantially eliminated, according to the method of the present invention when preparing emulsions with silver halide grains in the size range of from 0.1 micron to 5 microns by first mixing at least one of the aqueous salt solutions with a portion of the aqueous peptizer solution while isolated therefrom, and then introducing the peptizer-diluted salt solution into the remainder of the peptizer solution. A sufficient concentration of silver salt and halide salt is then provided by continued addition to the recirculated peptizer solution in the same manner to produce the desired silver halide grain formation.

The method of this invention is preferably carried out in the following manner to predictably form uniformly sized silver halide grains for a double jet emulsion. First an aqueous silver salt solution is diluted with a portion of a gelatin peptizer solution, simultaneously an aqueous solution of a halide salt is diluted with a separate portion of the peptizer solution while isolated from the diluted silver salt and both are isolated initially from the remainder of the peptizer solution. The two separately diluted portions are then introduced into the remainder of the peptizer solution preferably at a point below the surface thereof and in such a manner that the diluted solutions are substantially separate from each other until they are brought into reacting contact within the bulk of the peptizer solution. By this method the formation of uniform grain size from concentrated salt solutions is substantially enhanced. The reaction is continued by recirculation of portions of peptizer-product slurry by means of the apparatus of this invention to separately dilute the silver salt and halide salt solutions before introduction of the reactants into the bulk of the peptizer-product mix, preferably in contiguous streams.

The above as well as further advantages of the present invention will be more completely understood from the following description of preferred apparatus for practicing the herein described method. Reference is made to the drawings wherein:

FIG. 1 is a side elevation partly in section of a mixing apparatus according to the present invention.

FIG. 2 is a partially sectioned view of the top of the mixing chamber shown in FIG. 1.

FIG. 3 is a sectional view taken along the lines and arrows 33 of FIG. 2.

FIG. 4 is a side elevation partially in section of another mixing apparatus embodiment of the present invention.

FIG. 5 is a partially sectioned view of the top of the mixing chamber shown in FIG. 4.

FIG. 6 is a sectional view taken along the lines and arrows of FIG. 5.

Referring now to the embodiment of this invention shown in FIGS. 1, 2 and 3, it will be seen that a centrifugal mixing device 10 is provided which includes a rotatably mounted shaft 12, connected to an electric motor 14. The motor is mounted on a bracket 16 which is attached in a suitable manner to the mixing tank or vessel 20. The mixing device 10 is further provided with a housing 18 which is rigidly supported by rod 22 to the motor bracket 16. The housing 18 is provided at its top with inlet pipes 24 and at its bottom with inlet pipes 26 which communicate with the interior of housing 18. Outlet ports 28, provided with bafiles 30, located in spaced relationship generally around the middle circumference of housing 18.

The interior of mixing device 10 is shown in detail in FIG. 3. A double conically shaped mixing head 36 is attached to shaft 12 and is provided with an upper portion 38 which slopes inwardly above the supporting ring 34 and is provided with exit slots 40 and interior baffies 42. Likewise, the bottom portion 44 of mixing head 36 is similarly provided with slots 40 and baflles 42. Support ring 34 is a flat solid, non-perforated disk separating the upper portion 38 from the lower portion 44 and is disposed within the housing 18 in a position to roughly divide the housing into two halves, the intersections of two halves being roughly provided to coincide with the outlet ports 28.

FIG. 2 is a top view of the circular housing 18 showing the approximate location of slots 40, bafile plates 42 and the annular opening 46 around the shaft 12 into which the inlet pipes 24 empty.

It can be seen from an inspection of the mixing device 10 of FIG. 3 that reactants, such as an aqueous silver salt solution and an aqueous halide solution, can be introduced alternatively through either top pipes 24 or bottom pipes 26, respectively, from where they will enter by the action of rotation of the mixing head into the zone defined by the support ring 34 and the upper half or lower half of housing 18. Adjustment of the size of the annular opening 46 around shaft permits introduction of a portion of the bulk peptizer solution into the housing 18 under the influence of the rotating mixing head 36 with its bafiles 42, and ports 40. In this manner the aqueous silver solution is premixed in one half of the housing 18 with a portion of the bulk peptizer solution while halide salt solution is premixed in another portion of the housing 18 with a separate portion of the bulk peptizer solution. Both prediluted reaction streams are then forceably ejected through outlet ports 28 by the centrifugal force applied by the mixing head 36 a d d p into the bulk of the remaining peptizer solution by baffles 30. It is demonstrated hereinafter that separate premixing of a portion of the peptizer solution with each of the reactants and subsequent contiguous ejection of the diluted reactants permits the successful handling of higher concentrations then previously possible of each of the reactants described hereinbefore. This is accomplished simultaneously with the prevention of aggregate silver halide crystal formation within the bulk of the peptizer solution as the reactants come together and silver halide is precipitated within the vessel 20. At the required time the vessel may be evacuated by means of the open end provided at 48 in FIG. 1.

Dilution of fresh salt solution is also possible using recirculated peptizer-procluct slurry until the optimum time of run is achieved. The feed of reactants and peptizer to the mixing chambers can be by action of the mixing head as disclosed or by the use of supplemental equipment such as pumps where necessary. Likewise the optimum size for openings and pipes as well as their placement may vary from those shown where design changes are eifected.

Another mixing apparatus embodiment of the present invention is shown in FIGS. 4, 5 and 6. The structure for this mixing apparatus is similar to that shown in FIGS. 1, 2 and 3 in that the mixing device 60 has protruding through the top thereof, the shaft 62 connected to a motor 64 which is attached to the top of the mixing tank or vessel 70 by means of a bracket 66. The housing 68 of the mixing device 60 is supported beneath the liquid level' of the fluid vessel 70 by means of a supporting rod 72.

The housing 68 is provided at its top with inlet ports 24 and at its bottom with inlet ports 26. Outlet ports 78 are located generally around the middle periphery of housing 68.

The interior of mixing device 60 is shown in detail in FIG. 6. A two zone mixing head 86 is attached to shaft 62 and is provided with an upper zone containing perforated mixing vanes 87 attached to shaft 62 and a lower zone with similar perforated mixing vanes 87. The vanes 87 in both zones may also be attached to support plate 34. Support plate 34 is a flat solid disk separating the upper zone from the lower zone and is disposed within the housing 68 in a position which roughly divides the housing into two halves, the intersections of the two halves roughly coincides with the middle of outlet ports 78.

FIG. 5 is a top view of the generally square housing 68 showing the approximate location of the outlet ports 78 and the annular opening 46 around the shaft 62 into which the inlet pipes 24 empty.

The invention is further illustrated by reference to the following examples of preferred embodiments thereof. It should be understood that these examples are included for purposes of illustration and that specific amounts, techniques and the like are not intended to be construed as limiting in any manner the scope of the invention as disclosed hereinbefore.

EXAMPLE 1 A single jet silver bromoiodide gelatin emulsion containing 6 mole percent iodide is prepared in the following manner using a device similar to that shown in FIG. 1. Aqueous halide gelatin solution containing 76.8 grams of potassium iodide and 866 grams of potassium bromide is adjusted to a total volume of 242 ounces and thereafter maintained at F. throughout the precipitation reaction. An amount of silver nitrate, 1188 grams, is then dissolved in a total volume of 182 ounces of distilled water. This volume is introduced into the mixing chamber of FIG. 1 over a period of 20 minutes while the chamber is located below the surface of the previously prepared aqueous halide gelatin solution, and while the motor 14 is operating the mixing device 10. The resultant emulsion is washed by the coagulation procedure described in Yutzy et a1. U.S. Pat. 2,614,968. An aqueous gelatin solution is added to the washed coagulant resulting from the coagulation procedure in order to obtain the desired consistency. The total gelatin emulsion is then dispersed at 104 F. and a pH of 6.4. After dispersion the emulsion is sulfur and gold sensitized by conventional techniques and then heated for several minutes at 150 F., cooled to 104 F. and coated, with appropriate couplers, spreading and hardening agents onto a cellulose acetate support.

For comparison with the foregoing, an aqueous gelatin solution containing 433 grams of potassium bromide and 38.4 grams of potassium iodide is adjusted to a total volume 182 ounces. A halide gelatin solution is then heated to 151 F. and held at that temperature throughout the precipitation. An amount of silver nitrate, 594 grams. is dissolved in enough distilled water to make a total volume of 225 ounces. This silver nitrate solution is then added to the surface of the halide gelatin solution over a period of 40 minutes while the halide gelatin mixture is stirred vigorously with conventional motor driven stirrers. This emulsion is likewise washed by the coagulation procedure identified hereinbefore and additional aqueous gelatin solution is added to the washed coagulant to obtain the desired consistency and the gelatin emulsion is then dispersed at 104 F. and a pH of 6.4. This emulsion is also sulfur and gold sensitized in a conventional manner, heated for several minutes at 150 F., cooled to 104 F., and then coated with appropriate couplers, spreading and hardening agents onto a cellulose acetate support.

Coatings prepared as hereinbefore described were exposed on an intensity scale sensitometer for of a second at 285 0 K., identically developed, washed and dried in the conventional manner to produce the following tabular results.

Coating Relative number Gamma Dmnx. Dmin. speed A coarse grain silver bromoiodide gelatin emulsion containing 6 mole percent iodide is prepared according to the present invention using the agitator shown in FIG. 4. The aqueous halide gelatin solution containing 19.6 grams of potassium iodide and 922 grams of potassium bromide is adjusted to a total volume of 225 ounces. This solution is held at 135 F. throughout the precipitation. A quantity of silver nitrate, 1188 grams, is then dissolved in an aqueous solution having a total volume of 166 ounces. The reactant is introduced into a gelatin solution below its surface by means of a separate mixing chamber shown in FIG. 4 until the elapsed time of premixing and introduction into the gelatin is 20 minutes. The resultant emulsion is then washed by the coagulation procedure described in Yutzy et al. US. Pat. 2,614,968. Additional aqueous gelatin solution is added to the washed coagulant to obtain the desired consistency and the resultant emulsion is dispersed at 104 F. and a pH of 6.4. This emulsion is sulfur and gold sensitized in the conventional manner and heated for several minutes at 150 F., cooled to 104 F. and coated with appropriate spreading and hardening agents on a cellulose acetate support.

For comparison, an aqueous gelatin solution containing 461 grams of potassium bromide and 9.8 grams of potassium iodide is adjusted to a total volume of 186 ounces. A separate aqueous solution containing 594 grams of silver nitrate is adjusted to a total volume of 255 ounces. Silver solution is then added to the gelatin solution which is maintained at a temperature of 144 F. The addition lasts 40 minutes. The gelatin mixture is stirred throughout with a conventional motor-driven propeller mounted on the end of a shaft. The emulsionwas washed by the coagulation procedure described hereinbefore and coated in the same manner. Samples of each coating are ex posed on an intensity scale sensitometer for of a second at 2850 K., developed in the conventional manner, washed and dried with the following results.

Coating Relative number Gamma Dmnx. Dmin. speed It can be seen from the above tables that the emulsion from the first run prepared by the method and apparatus of the present invention using less time and lower temperature and with increased concentration of reactants than the second run, exhibits photographic results equal to the emulsion of the second run which is prepared by conventional methods.

EXAMPLE 3 EXAMPLE 4 A single jet coarse grain silver bromoiodide gelatin emulsion containing 6 mole percent iodide is prepared in a conventional manner (as described in Example 1), except for the following changes. An aqueous gelatin solution containing 866 g. of potassium bromide and 76.8 g. of potassium iodide is adjusted to a total volume of ounces. Silver nitrate (1188 g.) is dissolved in enough distilled water to make a total volume of 90 ounces and added to the surface of the halide gelatin solution over a period of 40 minutes.

The results of the above emulsion, after coating and processing as described in Example 1, displayed a high level of fog which appears on the processed print as pepper fog.

An emulsion was prepared using the concentrations previously described in this example and the agitating device as shown in FIG. 3. Only one chamber of the mixer is used. The results, after processing as described in Example I, shows no appreciable fog.

Apparatus similar to FIGS. 1, i2 and 3 employing half of the mixing head are useful in preparing single jet type emulsions. Likewise, the entire mixing head can be used for single jet type emulsions where both top and bottom inlet pipes feed the same reactant.

In the method of precipitating silver halide crystals according to the present invention it is advantageous for the pAg and/or pH of the peptizer-silver halide mixture to be continuously monitored and controlled by the proportional addition generally as hereinbefore described of silver salt solutions and/ or halide salt solutions in response to changes in pAg. Exemplary of pAg control means are the disclosures in US. Pat. 3,031,304 and Belgian Pat. 727,189. Likewise, the article by F. H. Claus and W. Pellaers, Crystal Habit Modification. of AgBr by Incorporation of Mom, Photographische Korrespondez, 103. Band, 1967, discloses useful control means. Such control can be carried out in an interrupted manner, a continuous manner or a semi-continuous manner consistent with the total precipitation procedure of the present invention. The pAg of the system can be determined by methods commonly used in the trade and is mathematically expressed as the negative logarithm of the silver ion concentration in moles per liter. The pAg is conventionally obtained by measuring the diiference between a reference electrode and a so-called pAg electrode which can be a silver electrode.

The silver halide emulsions which can be made from silver halide prepared according to this invention include silver chloride, silver bromide, silver bromoiodide, silver chlorobromoiodide, or mixtures thereof. The emulsions may be coarse or fine grain such as fine grained silver chlorobromide emulsions and fine grained monodispersed silver halide emulsions of the type described in Illingsworth U.S. application Ser. No. 500,366, filed Oct. 21, 1965, and now abandoned (French Pat. 1,497,202 issued Aug. 28, 1967). These emulsions can be prepared by any of the well-known procedures, e.g., single jet emulsions, double jet emulsions, such as Lippman emulsions, ammoniacal emulsions, thiocyanate or thioether ripened emulsions such as those described in Nietz et al., U.S. Pat. 2,222,264, Illingsworth, U.S. Pat. 3,320,069, and Mc- Bride, U.S. Pat. 3,271,157. Surface image emulsions may be used or internal image emulsions such as those described in Davey et al., U.S. Pat. 2,592,250; Lowe et al., U.S. Pat. 3,206,313; Berriman et al., U.S. Pat. 3,367,778, and Bacon et al., Belgian Pat. 704,255, as well as buried iodide emulsions of the type described in Porter et al., U.S. application No. 648,225, filed June 23, 1967, and now U.S. Pat. No. 3,505,068 (Belgian Pat. No. 716,914 issued Aug. 31, 1968). If desired, mixtures of surface and internal image emulsions may be used as described in Lnckey et al., U.S. Pat. 2,996,382. Negative type emulsions may be used or direct positive emulsions such as those described in Leermakers, U.S. Pat. 2,184,013; Kendall et al., U.S. Pat. 2,541,472; Berriman, U.S. Pat. 3,367,778; Schouivenaars, British Pat. 723,019; Illingsworth, French Pat. 1,520,821; Ives, U.S. Pat. 2,563,785; Knott et al., U.S. Pat. 2,456,953, and Land, U.S. Pat. 2,861,885.

The sliver halide emulsions used with this invention may be unwashed or washed to remove soluble salts. In the latter case the soluble salts may be removed by chillsetting and leaching or the emulsion may be coagulation washed, e.g., by the procedures described in Hewitson et el., U.S. Pat. 2,618,556; Yutzy et al., U.S. Pat. 2,614,- 928; Yackel, U.S. Pat. 2,565,418; Hart et al., U.S. Pat. 3,241,969; and Waller et al., U.S. Pat. 2,489,341.

The emulsions used with this invention may likewise be sensitized with chemical sensitizers, such as with reducing agents; sulfur, selenium or tellurium compounds; gold, platinum or palladium compounds; or combinations of these. Suitable procedures are described in Shepard, U.S. Pat. 1,623,499; Allen, U.S. Pat. 2,399,083; Mc- Veigh, U.S. Pat. 3,297,447; and Dunn, U.S. Pat. 3,297,446.

This invention may be used to produce elements designed for color photography, for example, elements containing color-forming couplers such as those described in Frohlich et al., U.S. Pat. 2,376,679; Vittum et al., U.S. Pat. 2,322,027; Fierke et al., U.S. Pat. 2,801,171; Godowsky, U.S. Pat. 2,698,794; Barr et al., U.S. Pat. 3,227,554, and Graham, U.S. Pat. 3,046,129; or elements to be developed in solutions containing color-forming couplers such as those described in Mannes and Godowsky, U.S.

Pat. 2,252,718; Carroll et al., U.S. Pat. 2,592,243, and

Schwau, U.S. Pat. 2,950,970.

Further the emulsions capable of being prepared are useful in the preparation of multilayer photographic elements which may be orthosensitized or pan-sensitized with spectral sensitizing dyes. For instance, these emulsions can be spectrally sensitized by treating with a solution of a sensitizing dye in an organic solvent or the dye may be added in the form of a dispersion as described in Owens et al. French Pat. 1,482,774. Sensitizing dyes useful in sensitizing such emulsions are described, for example, in U.S. Pats. 2,526,632 of Brooker and White issued Oct. 24, 1950; 2,503,776 of Sprague issued Apr. 11, 1950; Brooker et al. U.S. Pat. 2,493,748 and Taber et al. U.S. Pat. 3,384,486. Spectral sensitizers which can be used include the cyanines, merocyanines, complex (trinuclear) cyanines, complex(trinuclear) merocyanines, styryls and hemicyanines. The cyanines may contain such basic nuclei as thiazoles, oxazoles, selenazoles, imidazoles. Such nuclei may contain sulfoalkyl; carboxyalkyl and alkylamino groups and may be fused to benzene or naphthalene rings either unsubstituted or substituted with halogen, phenyl, alkyl or alkoxy groups. The dyes may be symmetrical or unsymmetrical and may contain alkyl, phenyl or heterocyclic substituents on the polymethine chain. The merocyanine dyes may contain the basic nuclei mentioned above as well as acid nuclei such as thiohydantoins, rhodanines, oxazolidenedienes and barbituric acids. The acid nuclei may be substituted with alkyl groups, phenyl groups, carboxy, sulfo, or amino groups. The emulsions may contain super-sensitizing dye COIIlblnations such as those described in Brooker et al. U.S. Pat. 2,739,964; Carroll et al. U.S. Pat. 2,688,545; Carroll et al. U.S. Pat. 2,701,198; Van Lare U.S. Pat. 2,739,149; Fuji British Pat. 1,128,840 or the dyes may be supersensitized with ascorbic acid derivatives, azaindenes, cadmium salts, and organic sulfonic acids as described in McFall et al. U.S. Pat. 2,933,390 and Jones et al. U.S. Pat. 2,937,089.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

We claim:

1. A method of forming silver halide grains during the preparation of a silver halide photographic emulsion within a vessel containing a bulk of aqueous peptizer solution, the method comprising the steps of:

separately diluting within the bulk peptizer solution an aqueous silver salt solution with a portion of the bulk peptizer solution and an aqueous halide salt solution with another portion of the bulk peptizer solution; and

directing contiguous streams of the diluted solutions into the bulk peptizer solution to bring the diluted solutions into reacting contact for precipitating within the bulk peptizer solution silver halide grains of generally uniform size.

2. A method of precipitating silver halide grains by the reaction within a vessel containing a bulk of aqueous peptizer solution utilizing a mixing head within the bulk peptizer solution and having at least two non-communicating chambers and a plurality of exit ports common to the chambers, the method comprising the steps of:

introducing a flow of an aqueous silver salt solution and a first flow of the bulk peptizer solution into one of the chambers;

mixing the flows of the silver salt and peptizer solutions within the one chamber;

introducing a flow of an aqueous halide salt solution and a second flow of the bulk peptizer solution into the other of the chambers;

mixing the flows of the halide salt and peptizer solutions within the other chamber; and

ejecting the mixed solutions in each chamber as separate and generally contiguous streams through the common ports and into the bulk peptizer solution to bring the mixed solutions into reacting contact 3,782,954 9 10 for precipitating within the bulk peptizer solutions OTHER REFERENCES silver halide grains of generally uniform size' Making and Coating Photographic Emulsions, Zelik- References Cited man and Levi, 1964 (pp. 228-335).

UNITED STATES PATENTS 5 NORMAN G. TORCHIN, Primary Examiner 3,415,650 12/1968 Frame 96-94 A. T. SURO P'ICO, Assistant Examiner 3,519,426 7/1970 Hal-wig 9694 US. Cl. X.R., FOREIGN PATENTS 787,336 12/1957 Great Britain 9694 10 

1. A METHOD AND APPARATUS FOR ITS PRACTICE ARE DISCLOSED WHERE, UNIFORMLY SIZED SILVER HALIDE GRAINS ARE PRECIPITATED IN AN AQUEOUS PEPTIZER SOLUTION BY THE REACTION OF A SILVER SALT SOLUTION WITH A HALIDE SALT SOLUTIONS, WHERE AT LEAST ONE OF THE SOLUTIONS HAS BEEN MIXED WITH A PORTION OF THE PEPTIZER SOLUTION PRIOR TO ITS REACTION WITH THE OTHER SLUTION WITHIN THE REMAINDER OF THE PEPTIZER SOLUTION, APPARATUS IS DISCLOSED FOR PRACTICING THE METHOD OF THIS INVENTION INCLUDING AT LEAST ONE SEPARATE MIXING CHAMBER FOR 